HMAS AE1 was an E-class submarine of the Royal Australian Navy (RAN). She was the first submarine to serve in the RAN, and sank with all hands near what is now East New Britain, Papua New Guinea, on 14 September 1914, after less than seven months in service. Search missions attempting to locate the wreck began in 1976. The submarine was found during the 13th search mission near the Duke of York Islands in December 2017.

The E class was a version of the preceding D-class submarine enlarged to accommodate an additional pair of broadside torpedo tubes. AE1 was 181 feet (55.2 m) long overall, with a beam of 22 feet 6 inches (6.9 m) and a draught of 12 feet 6 inches (3.8 m). She displaced 750 long tons (762 t) on the surface and 810 long tons (823 t) submerged. The E-class boats had a designed diving depth of 100 feet (30.5 m), but the addition of watertight bulkheads strengthened the hull and increased the actual diving depth to 200 feet (61.0 m). The complement consisted of 34 men: officers and ratings.

The boat had two propellers, each of which was driven by an eight-cylinder, 800-brake-horsepower (600 kW) diesel engine as well as a 420-brake-horsepower (313 kW) electric motor. This arrangement gave the E-class submarines a maximum speed of 15 knots (28 km/h; 17 mph) while surfaced and 10 knots (19 km/h; 12 mph) when submerged. They carried approximately 40 long tons (41 t) of fuel oil, which provided a range of 3,000 nautical miles (5,600 km; 3,500 mi) at 10 knots (19 km/h; 12 mph) while on the surface and 65 nmi (120 km; 75 mi) at 5 knots (9.3 km/h; 5.8 mph) while submerged. AE1 had four 18-inch (460 mm) torpedo tubes, one each in the bow and stern, plus two on the broadside, one firing to port and the other to starboard. The boat carried one spare torpedo for each tube. No guns were fitted.

In February 1911, defence minister George Pearce announced that orders had been placed with Vickers Limited for two submarines. AE1 was built at Barrow-in-Furness, England, having been laid down on 14 November 1911 and launched on 22 May 1913 and commissioned into the RAN on 28 February 1914. After commissioning, AE1, accompanied by AE2, the other of the RAN's first two submarines, reached Sydney from England on 24 May 1914. Officers for the submarines were Royal Navy (RN) personnel, while the ratings were a mix of sailors drawn from the RN and RAN.

At the outbreak of World War I, AE1, commanded by Lieutenant Commander Thomas Besant, was part of the Australian Naval and Military Expeditionary Force sent to attack German New Guinea. Along with AE2, she took part in the operations leading to the occupation of the German territory, including the surrender of Rabaul on 13 September 1914. The submarine's involvement was recognised in 2010, following an overhaul of the RAN battle honours system, with the retroactive award of the honour "Rabaul 1914".

At 07:00 on 14 September, AE1 departed Blanche Bay, Rabaul, to patrol off Cape Gazelle with HMAS Parramatta. When she had not returned by 20:00, several ships were dispatched to search for her. No trace of the submarine was found, and she was listed as lost with all hands. The disappearance was Australia's first major loss of World War I.

After the discovery of the submarine in December 2017, Rear Admiral Peter Briggs, retired, said the likely cause of its loss was a diving accident. He added:

The submarine appears to have struck the bottom with sufficient force to dislodge the fin from its footing, forcing it to hinge forward on its leading edge, impacting the casing.